Nanocellulose-Mediated N,P-Codoped Graphene Hydrogels and Regenerable Alginate Electrolyte for High-Performance Flexible Supercapacitors with Broad Environmental Adaptability

With the growing demand for high-volumetric-performance, flexible, and sustainable energy storage devices for wearable electronics and extreme environments, we report a multiscale regulation strategy; this strategy employs high-concentration graphene oxide (GO) for bulk density tuning, diammonium phosphate for N,P codoping, and nanocellulose (NC) as a green nanospacer. Using this strategy, we successfully prepared the NC-NPGHs electrode, which has rich surface defects, a balanced dense porous structure, and an expanded interlayer spacing. Combined with a renewable sodium alginate (SA)-based gel electrolyte (SNGK), we developed high-capacity supercapacitors. Aqueous symmetric supercapacitors (ASSCs) based on NC-NPGH20 achieve 413.0 F cm–3 volumetric capacitance at 0.3 A g–1, with 79.19% rate retention at 20 A g–1 and 94.52% capacitance retention after 20,000 cycles. The SNGK electrolyte, with a dynamic hydrogen bond network, exhibits 90% water retention at 60 °C and broad temperature tolerance (−30 to 60 °C), enabling flexible solid-state supercapacitors (FSSCs) to deliver 204.5 F g–1 with excellent bending stability and recyclability. This system outperforms most reported carbon-based supercapacitors, offering a sustainable solution for high-performance energy storage.